In this study genetic parameters were estimated and the importance of genotype by feeding system interactions investigated for a range of health and fertility traits in dairy cattle. Data were from the Langhill Dairy Cattle Research Centre and two UK recording schemes, one a recording scheme operated by the Scottish Livestock Services Ltd. (SLS) and the other a health and fertility recording and management system, the Dairy Information System (DAISY). Genetic parameters for 305 day yield of milk and its components, health traits (mastitis, somatic cell counts (SCC), lameness and milk fever) and fertility traits (calving interval, days to first service and conception to first service) were estimated using data from DAISY and SLS. Heritabilities and correlations agreed well between the two data sets implying that the nature of the recording scheme had little effect on the parameter estimates obtained. Heritabilities for all health and fertility traits were less than 0.10 with the exception of SCC which had a heritability of 0.15. The genetic correlation between SCC and mastitis was estimated to be 0.65. Genetic correlations of health and fertility traits with production were in all cases unfavourable. Using these estimates, a breeding programme designed to maximise response in production was predicted to increase calving intervals, mastitis and lameness by 0.39, 0.27 and 0.13 genetic standard deviations per unit selection differential. Restricting these traits to zero genetic change was predicted to result in 11% less overall economic response in production than an unrestricted index. Genotype by feeding system interactions were investigated for a wider range of health and fertility traits using data from Langhill. Selection and control line animals housed and managed as one herd were assigned to either a high concentrate or low concentrate feeding system. There were no significant genetic line by feeding system interactions. However, regressions of the traits on pedigree index for fat plus protein yield (PI) were significantly different from zero for six measures of fertility and mastitis. It was concluded that selection for production has led to a deterioration in some health and fertility traits in UK dairy herds. This deterioration could be halted, or the situation improved by direct recording and selection. However, in the absence of a national recording scheme for health and fertility, an alternative would be to use predictor traits, as they are generally easier to measure and record and have higher heritabilities. Results from this study supports the use of SCC as a selection criterion for mastitis (on a small data set), but the regressions on sire predicted transmitting abilities for type were less conclusive. Therefore future research should investigate associations between health, fertility, production, type, SCC and other potential predictor traits more fully and compare the role of direct measurements of these traits or indirect predictions of them in national indices.